Coverage of mobile User Equipment (UE) in 3GPP′ LTE systems is an ongoing concern. The desire is to provide connectivity to UEs in marginal signal strength conditions without excessive power consumption requirements placed on the UE.
One task required by a UE when it wishes to camp on an LTE cell is to perform cell synchronization. Synchronization includes detecting the Primary Synchronization Signal (PSS) and the Secondary Synchronization Signal (SSS) transmitted by the cell's evolved NodeB (eNB) base station. The PSS is used to indicate the cell identity within a group of cells, and the SSS is used to indicate the cell identity group number. Three different PSS signals and 168 different SSS signals are typically available. An eNB may use a particular combination of both identifiers to convey its cell-ID. A hierarchical cell search is performed by the UE to identify the cell-ID by analysis of the particular PSS and SSS transmitted by the cell's eNB.
However, standard methods of detecting the PSS and SSS can consume relatively large amounts of time and energy, particularly in marginal signal conditions and/or when Discontinuous Reception (DRX) is employed by a UE.
There is a requirement for LTE Cat-M1 (LTE-M) and narrow band Internet-of-things (NB-IOT) to support a high maximum coupling loss (MCL), for example 164 dB. However, for resynchronization, for example resynchronization after a UE comes out of a deep sleep from power saving mode (PSM) or discontinuous reception (DRX) or extended DRX, where the cell providing service to the UE has not changed but the carrier frequency offset (CFO) and timing are unknown, it is difficult to achieve a similar high MCL and achieving the high MCL can take a long time using significant UE power and increased latency. FIG. 1 illustrates the performance of legacy PSS/SSS for resynchronization, under the assumption that the UE knows the SSS and PSS sequences. As can be seen in FIG. 1, the legacy PSS/SSS 90th percentile resynchronization can take approximately 2.5 seconds at 164 dB MCL. As such, the time period for resynchronization can be prohibitively long.
Therefore there is a need for a method and system for using enhanced Primary Synchronization Signals for resynchronization that is not subject to one or more limitations of the prior art.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.